Under a wireless LAN environment in which an IEEE802.11b standard using frequencies lying within a 2.4 GHz band and an IEEE802.11g standard having backward compatibility and providing further achievement of speeding up are existent in mixed form in a basic service set (BBS) including one access point (AP), the rate of transmission of its information is reduced. As its cause, the IEEE802.11b standard and the IEEE802.11g standard make use of the same frequency. The IEEE802.11g standard is a system developed after the IEEE802.11b standard. The IEEE802.11b standard recognizes radio waves based on the IEEE802.11g standard as noise. On the other hand, since the IEEE802.11g standard is normalized with being put emphasis on compatibility with the existing standard, it is capable of normally recognizing radio waves based on the IEEE802.11b standard. With this situation, carrier sense for confirming transmission of other terminal device in such a manner that the radio waves do not collide with each other is normally executed upon transmission of a wireless LAN. Depending upon the result of such carrier sense, transmission is started from a self terminal device. However, the terminal device of the IEEE802.11b standard is not able to recognize transmission of a terminal device of the IEEE802.11g standard. Therefore, the terminal device of the IEEE802.11b standard also starts transmission during a period in which the terminal device of the IEEE802.11g standard is in transmission. As a result, a collision occurs when they try to transmit, thus causing a reduction in transmission rate.
As described in, for example, a non-patent document 1 (“802.11 high-speed wireless LAN Text edited by Hideaki Matsue and Masahiro Morikura” issued on March, 2003, pp 75-77 and 170-171, IDG Japan Inc.), the conventional technique has solved such a collision by using a high-speed transmission mode based on the IEEE802.11g standard. This mode is used for the purpose of enhancing a transmission rate based on the IEEE802.11g standard. As described in the 170th page, Clear To Send (CTS) indicative of a transmit permission is used as this method. The CTS is a signal normally used to solve a hidden terminal problem as described in the 75th to 77th pages of the non-patent document 1. An AP or a wireless terminal (STAtion) based on the IEEE802.11g standard trying to transmit transmits CTS to a self destination according to the IEEE802.11b standard. When it transmits the CTS according to this standard, all STAs lying in the BSS, i.e., STAs based on the IEEE802.11b standard and STAs based on the IEEE802.11g standard are capable of recognizing the present CTS. In particular, STAs other than the STAs having transmitted the self-destined CTSs notify that the STAs having transmitted the self-destined CTS are ready for reception thereof. Thus, the STAs recognize the CTSs when they are trying to transmit, and put off their own transmission. Accordingly, each STA trying to transmit does not collide with other STAs and is able to transmit the CTS. Thus, the transmission rate is enhanced. According to the present method, an AP or each STA trying to transmit transmits a self-destined CTS for each packet.
Thus, the transmission rate is improved under the environment in which the terminals of the different groups capable of using the same radio channel are existent in mixed form. Therefore, there is proposed a wireless communication apparatus described in, for example, a patent document 1 (Japanese Unexamined Patent Publication No. 2003-18170) as a specific example. When the wireless communication apparatus is informed that carriers of other groups using the same radio channel has been detected upon communication with other wireless communication apparatuses using their corresponding radio channels of arbitrary radio channels, a first radio channel and a second radio channel in a predetermined radio frequency band, the wireless communication apparatus restrains and controls wireless communication means in such a manner that wireless communications with the corresponding wireless communication apparatus using the other radio channel, e.g., the transmission of carriers is brought to a halt, whereby the radio channel already in use is given priority to prevent a collision between the carriers.
Meanwhile, when the AP or STA transmits the self-destined CTS for each packet according to the existing technique, the self-destined CTS is transmitted based on the IEEE802.11b standard and hence the transmission rate is slow. Thus, when such transmission that the self-destined CTS is transmitted in plural form for each packet is taken, the present transmission can prevent collisions as compared with the normal transmission free of use of CTS and hence the transmission rate can be enhanced. However, time is taken by transmission of the self-destined CTS as overhead in addition to actual data transmission, thus resulting in inefficient transmission.